Packaging machines receive bag material in tubular form. Product to be packaged is delivered to the interior of the tubular bag material, with the packaging machine then transversely sealing and cutting the tubular bag material to form bags of product. The tubular bag material is formed by a former shoulder, to which packaging film is delivered in strip form. Formers and packaging machines are described in U.S. Pat. Nos. 4,910,943, 5,622,032, 4,663,917, 6,655,110, 7,159,376, 7,600,630, 7,383,672, 4,753,336, 7,124,559, 7,415,809, 7,152,387 and 7,472,528, and Australian Patent Applications 2012258403, 20122584, 2012258497, 2012201494 and 2012201595.
The tubular material provided by the former shoulder is longitudinally sealed. This function is performed by heating the tubular bag material along its longitudinally overlapping edges and by applying pressure to the overlapping longitudinal edges.
Located above the former is a weighing machine that delivers batches of product to a sleeve that extends to the former, with an internal sleeve extending from the central opening of the former to a position adjacent or below the lower edge of the former.
The tubular bag material passes the former that provides the former shoulder, is longitudinally sealed and then delivered to the packaging machine. While this is occurring batches of product are delivered to the interior of the tubular bag material by the weigher, the batches consisting of product scattered along a length of the tubular bag material. A film drive assembly is located below the former and above the packaging machine. The film drive assembly engages the tubular bag material to cause the strip material to pass over the former, and delivers the tubular bag material to the packaging machine below. Typically the film drive unit includes a pair of driven belts (or rollers) that drive the tubular bag material at a desired velocity. The packaging machine includes at least a pair of rotatably driven jaws, with the jaws having a peripheral speed (when engaged with the tubular bag material) that matches the velocity of the tubular bag material as determined by the film drive assembly.
The disadvantage of the above discussed machines is that due to the length of each product batch, the packaging machine is limited in respect of the number of bags it can produce per minute.
Product leaving the weighing machine, as mentioned above, is arranged in batches. It is not unusual for the batches to have a length of 100 ms when leaving the weighing machine. However the batches follow an arcuate path as they enter the former. This causes the product to impact against itself, and the internal surfaces of the tubular bag material. The result is that the product batches increase in length. As an example the batch length may increase to 600 ms. To ensure the product is not located between the sealing jaws, it is assumed, in programming the packaging machine, that the product batches have a length of about 650 ms.
The batches become elongated as the product falls through the former to the packaging machine below. The greater this fall length, the greater the batch elongation.
The elongated batches create a further problem in that it becomes difficult to minimise the volume of product in the bags being formed.
It is therefore a disadvantage of known packaging assemblies that the packaging machines cannot operate at maximum speed due to undesirable batch elongation.